As football fans gear up for Saturday's annual preseason battle between the Bay Area's NFL rivals, the 49ers and Raiders are joining forces off the field to discuss sharing a stadium as part of the billion dollar question no one can seem to answer: Where will the two teams play their home games five years from now?

Four California cities are vying to build new stadiums in hopes of luring one or both of the teams, with the eyes of millions of fans and taxpayers trained on the debate and untold riches and national prestige at stake.

So will Niners Nation share a new home with the Black Hole? Or will the teams move into separate stadiums in San Francisco, Oakland, Santa Clara or even -- gasp -- Los Angeles?

The recent NFL labor deal cleared the way for the league to help fund a new generation of stadiums, but like the teams' attempts to return to greatness on the field, the stadium saga remains frustratingly uncertain. There are, however, clear favorites and long shots.

The front-runner: Santa Clara. 49ers President Jed York said this week the team is "100 percent focused" on starting construction on a $987 million stadium next to the Great America amusement park in January 2013. He said the Niners will move forward with or without funding help from the Raiders, although the league is encouraging the teams to consider pooling their resources together to share a stadium like the Giants and Jets did for a new $1.6 billion home in New Jersey.

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The challenger: Oakland. "For several years,'' Raiders CEO Amy Trask said, "we have been quite vocal about our support for a new facility in Oakland." City officials last month unveiled a plan to want to transform the city's gray and sagging O.co Coliseum by building a new "Oakland Live" entertainment complex with hotels, bars, restaurants, shops and a convention center.

The back-up plans: San Francisco is banking on the 49ers abandoning Santa Clara and moving into a new home in the City by the Bay, while Los Angeles is trying to lure a team or two -- including possibly the Raiders -- to its forthcoming new stadium.

First quarter: Can it happen?

SANTA CLARA: There are two big remaining hurdles. The 49ers will need to beat out several other teams to be among the first to secure a league loan -- by the end of 2012 -- to open the field in 2015. Second, the 49ers and city must meet lofty goals to secure sponsorships and loans, and sell season tickets.

"I think we're getting very close," York said. "I don't think there is a rabbit that's going to get pulled out of a hat" to derail the plan.

OAKLAND: The Raiders could kick off in a brand-new football palace by 2016, but the city must complete planning reports by late next year. There is hardly any local funding available so far and despite new blood at City Hall, the political track record between the team and city has been filled with incomplete passes. Moreover, the Raiders will likely need to reverse their strained history with the league to score a huge NFL loan on top of what the 49ers could get.

SAN FRANCISCO: Even if it Santa Clara plan falls apart, the team will need to repair a rocky relationship with contentious San Francisco leaders, and figure out how to pay for the project. Yet it remains a strong Plan B.

LOS ANGELES: The Raiders' Trask declined to speculate about the possibility of relocating to Los Angeles if the Oakland plan fails, but experts say the team's need for a new stadium and its history in Los Angeles make the possibility intriguing. But L.A. developers may not get far demanding a stake in the team, as Trask said they are not for sale.

Second quarter: One team or two?

SANTA CLARA: While the Niners are designing their home for two teams, York hinted a shared stadium will be up to the Raiders, saying it's a question only their East Bay rivals could answer. If eccentric Raiders owner Al Davis is willing to put territorial and control issues aside, both teams could end up in the South Bay, but Trask said the team remains no closer in committing to move to the South Bay.

NFL spokesman Greg Aiello would only say that the league will fund multiple stadiums during the 10-year labor deal, likely including at least one in the Bay Area.

OAKLAND: This time, it's up to the 49ers. York would only say the team has been briefed on the Oakland plan but has not received a formal proposal to move there.

"The 49ers have said they are leaving San Francisco, period,'' said Oakland At-Large Councilmember Rebecca Kaplan. "The only question is, will their new location be (in Oakland) on BART?"

SAN FRANCISCO: "To be honest, (the stadium plan) is not strictly for the 49ers," said former 49ers CEO Carmen Policy, now a consultant trying to keep the team in San Francisco. "Ideally, it'd be for both the 49ers and the Raiders."

LOS ANGELES: The stadium could host one or two existing teams that would move to L.A., with speculation pointing at the San Diego Chargers and Raiders as possibilities.

Third quarter: Can they afford it?

SANTA CLARA: The team and city have $113 million in tax funds and $138 million in luxury suite sales for a $987 million stadium, and need to secure the rest in the next year-plus from the NFL, private loans, sponsorships and season tickets. Critics say that is only wishful thinking.

OAKLAND: With limited tax support and the Raiders not committing to spending their own funds, the team and city face a daunting fundraising drive. City leaders are trying to tap up to $105 million in county transit funds, have spent $30 million in redevelopment revenue to buy land and complete environmental plans, and have reported interest from investors such as Chinese government-backed HNA Group, but not much else for a $863 million stadium.

SAN FRANCISCO: Developer Lennar Corporation has pledged $100 million and the city has promised free land and parking to help fund a $1 billion project, Policy said. Still, the plan faces the same funding doubts as Oakland, and is further behind than Santa Clara.

LOS ANGELES: Money, here, is not an issue. Aided by a record naming rights deal from Farmers Insurance Group, likely city bond funds and deep pockets from developer AEG, the $1.2 billion Los Angeles stadium could start construction next year.

Fourth quarter: Will fans come?

SANTA CLARA: Loyal fans may groan about a venue change, but it should be much easier to drive to and park at Santa Clara than Candlestick Park, while 30 percent of season ticket holders already live in the South Bay. Fans may be able to visit Joe Montana's proposed hotel, bar and restaurant across the street, but there is not much else nearby yet -- besides a rollercoaster.

OAKLAND: In addition to easy freeway access, it has a leg-up with a BART stop and an existing loyal fan base.

"Here,'' said Oakland resident Sal Herrera, "all we want is" for the team to stay.

SAN FRANCISCO: Team history makes San Francisco the sentimental favorite for many fans.

"The sites with the view and the panache are quite spectacular, and this is the city where the team was born," Policy said. "The story plays out so well if they stay in their hometown."

LOS ANGELES: That would be sacrilege to fans. But if someone else moves there, it could resurrect a rivalry on par with the 49ers-L.A. Rams, York said. And for that reason, York calls himself "probably the biggest proponent" for an L.A. team.